Silver base alloy



Patented June 6, 1939 PATENT OFFICE 2,161,576. smvna BASE ALLOY Franc a. Hensei, Kenneth L. Emmett, and James W. Wigg's, Indianapolis, Ind, assignors'toP. R. Mallory & Co., 'Inc., Indianapolis, Ind., a corporation of Delaware No Drawing. Application April 13, 1939,

' Serial N0. 267,607

4 Claims. (01. 75-179 This invention relates to a new silver alloy and is concerned more particularly with an alloy which has improved physical and electrical characteristics.

5 It is one of theobjects of the invention to provide a silver base material which can be used .for an clectricalmake and break contact, re-' taining very low contact resistance, having very low material transfer and being free from weldl ing and sticking under heavy electrical loads.

Another object of the invention is to provide a new silver base alloy which has improved tensile properties and which also shows considerable improvements as far as corrosion resistance is l concerned.

Other objects of. the invention will be apparent from the followingdescription, taken in connection with the appended claims.

The present invention comprises a combination of elements, methods of manufacture and the products thereof, brought out and exempliiied in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.-

5; While a preferred embodiment of the invention is described herein, it is contemplated that a considerable variation may be made in the method of procedure and the combination of elements, without departing from the spirit of the invention.

- The present invention relates to an alloy of silver, magnesium and thorium. In the formation of the new alloy, it is preferable to provide a composition of the materials specified in the 5 following proportions:

a Per cent Magnesium; .05 to 15- Thorium .005 .to 10 Silver 4 ;Bal ance 40 It is likewise possible to improve the characteristics of silver alloys containing a'ddltlonalingredients by the combined addition of magneslum and thorium. Such elements are primarily copper and gold, zinc, cadmium, indium, thallium, zirconium and tin. We have also found that iron group metals may be added up to several percentages, and that the alloys may con- -tain considerable percentages of precious metals, taken from the palladium and platinum group.

f A preferred range of magnesium is .05 to 8%, because up to that percentage, magnesium is taken up in alpha solution in silver and we have found that silver and magnesium, up'to 8%, can

be alloyed very readily, and the cast ingots can be rolled, swaged or drawn into desirable shapes,

such as sheet, bar stock, wire, strip and the like. A more specific preferred range for magnesium is 1 to 4%. .1 to 3%.

The addition of thorium to silver magnesium base alloys further improves the physical and electrical characteristics. Thorium has a very high meltingpoint and one of its outstanding properties is the great deoxidizlng power, resulting in completely deoxidized'and clean silver alloys, which are of advantageparticularly in their use as electricalcontactingelements, inorder to prevent localized build-up. Thorium was introducedinthe form of a silver thorium master alloy, having a high concentration of thorium and being prepared -by powder metallurgical methods. No difiiculty was encountered in absorbing thorium in the-silver.

We have investigated a series of. compositions and have found that the following alloys which are given by way of example have shown very excellent physical properties,.and particularly electrical properties, if used in the form of elec- These ingredients in the proportions named above, --are melted together and poured into a suitable mold. It was pointed out above that it was found desirable to add the thorium in the form of silver-thorium master alloy. It was also found desirable to add 'the magnesium in the form of a silver-magnesium master alloy, of high magnesiumconcentration. Master alloys of this suitable fluxes which cover the melt.

The addition of magnesium in the form of a master alloy has also reduced the loss of magnesium and therefore has made it possible to 'holdcloser tolerances in the chemical composition. i

A preferred range for thoriumis and form An alloy containing, for instance, 3% magnesium and 2 thorium, was prepared by such melting methods as just .outlined, and in the cast condition, showed a Rockwell F. hardness of 55. The material 'could be readily s'waged and after a reduction of 30% increased in hardness to 94 F. The electrical conductivity of a material of such composition was 22.4% International annealed copper standard.

The superior qualities of alloys described by the present invention for electrical purposes; are illustrated by the following examples: A comparison test was conducted, wherein contacts of similar physical dimensions were tested on a resistive inductive circuit at 470 cycles ,per minute and wherein the current flowing in the circuit was increased periodically to obtain the definite current values of alloys in the nature described above, in comparison with contact materials in the prior art. The amount of material transfer of one contact to the other was -also used as a method of comparison.

Contacts'of the following .compositions, when operated under the above stated conditions, gave outstanding performances compared to the alloys of the prior art, some of which are given for comparison:

The final contact resistance on these new and, improved alloys, the composition of which are givenabove, did not substantially exceed the values obtained for-fine silver, under identical test conditions. The alloy containing, for instance, 3.% magnesium and 2%% thorium,

that the metallic transfer, due to the operation I of these contacts, is considerablysmaller than on fine silver/ "Also, this reduction'in transfer has been obtained in spite of the fact that the new alloys were operated at much higher current values, and therefore under much more severe transfer producing conditions. It should also be 5 noted that the limiting current, .that is, the current at which the contacts-tends to weld together, is considerably higher than that of fine silver, the value for fine silver being 12 amps,

and that for the improved alloy, 19 amps.

The alloys of the present invention have been found useful, for a large number of electrical contact applications, such as, for instance, sensitive direct current relays, over-load cutouts,

voltage. regulators; indicating and recording 5 gaugers, thermostatic controls and the like. v Other uses of the new alloy are in the form of silverware, such as is used for table ware, industrial applications, jewelry purposes andthe like.

The alloy of the present invention has also a 20 commercial advantage-because the addition of magnesium in the percentage contemplated,

provides a material of lower specific gravity'and therefore it is possible to produce a larger num-' ber of finished products per unit weight of ma- 2'5 terial.

While the present invention as to its objects and; advantages has been described herein, as carried out in specific embodiments thereof, it is not desired to be limited thereby, but it is in- 30 balance r 3. An alloy of 1 to 4% magnesium, .005 to 10% thorium, and the entire balance substantially all silver.

4. An alloy of 1 to 4% magnesium, .1 to 3% thorium, and the balance substantially all silver.

FRANZ'R. HENSEL. f

KENNETH L. ElVllViERT. JAMES W. WIGGS. 

